TAMPA, Fla. — Clint Eastwood’s rambling and off-color endorsement of Mitt Romney on Thursday seemed to startle and unsettle even the candidate’s own top aides, several of whom made a point of distancing themselves from the decision to put him onstage without a polished script.

“Not me,” said an exasperated-looking senior adviser, when asked who was responsible for Mr. Eastwood’s speech. In late-night interviews, aides variously called the speech “strange” and “weird.” One described it as “theater of the absurd.”

Finger-pointing quickly ensued, suggesting real displeasure and even confusion over the handling of Mr. Eastwood’s performance, which was kept secret until the last minute and offered an off-key message on the night that Mr. Romney accepted the Republican presidential nomination.

A senior Republican involved in convention planning said that Mr. Eastwood’s appearance was cleared by at least two of Mr. Romney’s top advisers, Russ Schriefer and Stuart Stevens. This person said that there had been no rehearsal, to the surprise of the rest of the campaign team.

But another adviser said that several top aides had reviewed talking points given to Mr. Eastwood, which the campaign had discussed with the actor as recently as a few hours before his appearance. Mr. Eastwood, however, delivered those points in a theatrical, and at times crass, way that caught Romney aides off guard, this person said. Mr. Eastwood even ignored warnings that he had exceeded his time.

Mr. Stevens, in an interview, said he would not discuss internal decision making but described Mr. Eastwood’s remarks as improvised.

“He spoke from the heart with a classic improv sketch which everyone at the convention loved,” Mr. Stevens said.

He called it “an honor that a great American icon would come and talk about the failure of the current president and the promise of the future one.”

Mr. Eastwood delivered one of the more unusual moments in Republican convention history — a speech in which he pretended to have a sarcasm-filled conversation with President Obama sitting by his side in an empty chair. Initially, there were no plans for Mr. Eastwood to take a chair onstage as a prop. But at the last minute, the actor asked the production staff backstage if he could use one, but did not explain why. “The prop person probably thought he was going to sit in it,” a senior aide said.

“Mr. President, how do you handle promises that you made when you were running for election?” the onetime Dirty Harry said, mumbling to a befuddled crowd of thousands in the convention hall and millions of television viewers.

As thousands of “OMG!” tweets started flying, Mr. Eastwood, 82, asked the invisible Mr. Obama why he had not closed the prison at Guantánamo Bay, Cuba.

“What do you mean, shut up?” he said, continuing to talk to his imaginary companion. A moment later, he stopped again, saying, “What do you want me to tell Mr. Romney?”

“I can’t tell him that. He can’t do that to himself,” Mr. Eastwood said. “You’re getting as bad as Biden.”

Leonard Hirshan, Mr. Eastwood’s manager, said the actor was traveling and would not be available for interviews until he started promotional work shortly for his next film, “Trouble With the Curve,” which is set for release by Warner Brothers on Sept. 21.

Mr. Hirshan said he had heard a chorus of response since the speech, divided evenly between those supportive and critical. “The more I look at it, the more I appreciate what he did,” said Mr. Hirshan, who added that neither he nor others in Mr. Eastwood’s professional entourage, as far as he knew, were consulted in advance.

“He does these things for himself,” said Mr. Hirshan, who spoke by telephone on Friday morning. “It’s his private life. He believes in what he’s doing.”

The networks began their hour of convention coverage at 10 p.m. Eastern time, which meant that Mr. Eastwood was the first act of the night for their viewers. He was scheduled to speak for about five minutes but stayed onstage much longer, throwing off the schedule for Mr. Romney, a stickler against tardiness.

As Mr. Eastwood ran long, convention producers activated a red light on the camera stand opposite the stage, a signal to nudge speakers to wrap up their remarks.

Despite the fuss that the speech created, the campaign insisted that Mr. Romney enjoyed it.

“I was backstage with him and he was laughing,” Mr. Stevens said.

Aides said Mr. Eastwood does not like teleprompters and was trusted to deliver an on-message endorsement.

“He made a last-minute decision to ad-lib, and I don’t think people knew,” said Ari Fleischer, a former adviser to George W. Bush, who said he had spoken with people involved in planning the convention. He suggested that second-guessing of the Romney campaign’s convention presentation was “just the nature of the beast.”

Two aides said that Mr. Eastwood had been booked weeks ago and that the expectation was that he would deliver a more standard endorsement, as he did earlier this year in Sun Valley, Idaho.

After that endorsement, Mr. Romney himself asked Mr. Eastwood to come to the convention, one of these people said.

Advisers were quick to point out that Mr. Eastwood mentioned all the points they had agreed upon, including an unemployment figure, but the aides had expected him to address the issues in a more straightforward manner.

As they hopped from party to party late Thursday and early Friday, celebrating the end of the Republican convention, Romney advisers tried gamely to find an upside. Several said that the Eastwood appearance offered a moment of improvisation in a convention that was otherwise surprise-free.